Rhythmic Masseter Twitches In REM Sleep Of The Guinea Pig

Abstract

Objectives: Repetitive muscle twitches were reported to occur in face and limb muscles in rapid eye movement (REM) sleep. The aim of present study is to assess burst patterns of REM twitches in masseter muscle in guinea pig.

Methods: Five young adult guinea pigs were recorded with electroencephalogram (EEG), electro-occulogram (EOG) and electromyograms (EMGs) from the dorsal neck and masseter muscles. Sleep stages were scored by EEG EOG and neck EMG according to the standard criteria. The duration and integrated activity were analyzed in addition to the burst intervals. Variability of the burst intervals was assessed by coefficient of variation. These variables were compared between chewing and REM twitches.

Results: REM twitches in masseter muscle usually occurred in a cluster. The duration of REM twitches was significantly shorter (0.08 0.01 sec) than those of bursts during chewing (0.11 0.03 sec) (p<0.05). The integrated activity of the bursts associated with REM twitches was approximately half of bursts during chewing (p<0.05). However, the burst interval did not differ between REM sleep (0.37 0.04 sec) and chewing (0.36 0.05 sec), characterized by a larger variability of the burst interval for REM twitches (0.56 0.06) than for chewing (0.22 0.06) (p<0.05). Large variability of the burst interval in REM twitches was associated with an intermittent burst loss within a cluster of bursts.

Conclusion: REM twitches in masseter muscle exhibit a rhythmic pattern analogous to the bursts during chewing. This suggests that masseter motoneurons receive rhythmic facilitatory inputs under tonic motor inhibition in REM sleep. Intermittent burst loss within a cluster of REM twitches is probably due to phasic inhibition onto the motoneurons in REM sleep. Supported by the JSPS.